Signaling system



D. MITCHELL SIGNALING SYSTEM Filed Dec. 29, 1935 Jan. 7, 1936.

ATTORNEY INVENTOR Mchte@ BY I A I I I f Y I I Y 7; l m N+ NMMNWEQ @wwwNmwww mN+ III l II I I I I I I I I I I I Patented Jan. 7, 193.6

t UNITED sTATEs SIGNALING SYSTEM Doren Mitchell, Bound Brook, N. VJ.,assigner to American Telephone and Telegraph Company, a corporation ofNew York Application December 29, 1933, Serial No. '104,557

35 claims. (c1. 17a- 44) Thisinvention relates to signaling systems, andmore particularly to signaling systems in which either carrier energyorspecial control energy is applied to the transmitter only during theperiods of signal transmission. With greater particularity, theinvention relates to carrier systems of the type indicated in which thegain of the receiver is automatically controlled by the received carrierenergy. An example of the systems to which the invention is applicableis a short-wave transoceanic radio system in which it is desirable thatthe carrier be removed when no signal energy is applied to thetransmitter and that the receiver gain be controlled by the carrierenergy. It is to be understood that the invention is equally applicableto systems in which the control is effected by a special frequency wavewhich is not the carrier.

In systems of the indicated type as operated heretofore, when thecarrier (or other control energy) is removed from the transmitter, thereceiver gain may rise by decibels or even a greater amount; when thecarrier is again applied to the system, it becomes necessary to reducethe receiver gain before signal waves can be received withoutconsiderable distortion due to overloading. Since it is generallydesirable to make the gain adjusting action relatively slow, in order toavoid excessive hunting in the gain control de- 'Vice and the resultantdistortion, there may be a period of several seconds after the carrieris reapplied which is marked by the distortion of the signal due to theexcessive gain of the receiver.

The principal object of the invention is to reduce as far as possiblethe distortion heretofore introduced in the receiver in connection withthe removal of the carrier or other control energyand the subsequentre-application of that energy. Subordinate objects are to provide for areceiver 1 gain of a desirable value when the carrier isv removed and toprovide for the quick readjustment of that gain when the carrierA isagain received, possibly with a widely different value.

In general, the above-stated objects are attained by novel methods andmeans whereby, when the carrier or other control energy is removed, thereceiver gain is either maintained at its last value or, if the carrieris off for a predetermined time, brought to some other predeter- 'minedvalve, and, when that energyagain arrives, the receiver gain is quicklyreadjusted to the new carrier or other control energy intensity, withoutthe delay which would normally be introduced by the slow action of thegain adjusting device.

The invention will be clearly understood when the following descriptionof one desirable arrangement of the circuits and of the operationthereof is read with reference to the accompanying drawing, of which-Figure 1 shows schematically a signaling system in which thecarrier isapplied at the transmitter only when signal energy is to be transmittedand in which the received carrier controls the receiver output path andvthe receiver gain, and indicates the novel features introduced by theapplicant;

' Fig. 2 shows diagrammatically a suitable arrangement of the receivercircuits; and

Fig. 3 shows diagrammatically a modification of the circuits of Fig. 2to suit the case of control energy other than the carrier.

With reference to the schematic disclosure of Fig. 1, there is indicateda signaling system including a transmitting station W at the left and areceiving station E at the right. The system specifically indicated is aradio system but it will be understood that the transmission fromstation W tostation E might as well be over wires. When there is nosignal to be transmitted, the oscillator is disassociated from themodulator at the transmitting station W. At the receiving station E,there is indicated a receiver having a demodulated signal path which maybe controlled at a point b. When no signal is applied to the system,

this demodulated signal path is disabled at4 point b.

If signal is transmitted, energy is diverted at point a at thetransmitting end and serves to connect the oscillator with themodulator. After being ampliiied and radiated from the station W, thisenergy is received at the station E. There areindicated schematically atthe station E a codanthat is, a carrier operated device antinoiseandautomatic gain control apparatus. When the carrier energy is received atthe station E, energy istaken from the receiver circuit to y operate thecodan and the automatic gain control circuit. The eifect of theoperation of the codan is to remove the disability at point b and thusrender the receiver output operative. It will be noted that normally theoutput of the automatic gain control is disassociated from the receiver.When, however, the carrier energy arrives, an operation at` point cserves to connect the output of the gain control with the receiverinput. As is indicated by the condenser, provision is made, inaccordance with the applicants invention, for some normal control of thereceiver gain in the absence of the connection of.

the automatic gain control output with the ceiver input.

Thus, by the schematic showing of Fig. 1, there is indicated a signalsystem in which the carrier is applied at the transmitting end onlyunder the control of the signal; when the carrier reaches the receivingend, the normally disabled demodulated signal path is rendered operativeand the gain of the receiver is controlled by the incoming carrier. Inthe absence of the reception of carrier energy, however, a certaincontrol. is exercised over the receiver gain.

In Fig. 2, there is shown diagrammatically and, in part, schematically,one desirable arrangement of the receiver circuits. It will. beVunderstood that the carrier energy is applied to the system and itsapplication interrupted in the manner indicated in Fig. l. The pertinentportions of the complete receiver circuit are shown as a high frequencyamplier, a first detector, an intermediate frequency ampliiier and lter,a second detector and an audio-frequency amplifier. The output of theaudio-frequency amplifier or, in other words, a portionof thedemodulated signal path is designated L. Those` portions of the completecircuit which make up the codan and the automatic gain control deviceare appropriately indicated. A relay chain comprises the codan relay S1,a relay S2, which may be called the gain-maintaining relay, and a relayS3, which is preferably slow-operating and slow releasing and may becalled the quick gain control relay. It should be noted that thecircuits are shown in the condition produced by the reception of carrierenergy at the receiving station; accordingly, relays S1, S2 and Ss arein released condition and the path L is operative.

' The apparatus already mentioned', along with ..certain condensers,resistances and batteries,

make up the circuits arranged in accordance with the applicantsinvention, except that certain elements may be added in accordance witha modification to be described hereinafter. It is believed that thedetails of thev circuits will be best understood-from a reading of thefollowing discussion of the operation.

Received carrier energy causes current to flow in the circuit ofthesecond detector, which includes a resistance R1. WhenY current owsthrough resistance R1 toground, the grids of the two vacuum tubesTandT1, whichV are connected to resistance R1, become negative withrespect to ground. In tube T, which forms a part of the codan circuitthevoltage on the grid is adjusted so that, with the reception'of carrier,it will be sumciently negative to reduce the plate current ofr tube Tsubstantially to zero. Accordingly, relays S1 and S2 have no appreciablecurrent in their windings and are in the released condition. The releaseof relay S1 removes the disability normally applied to the path L andincoming transmission is permitted to pass on over thereceivingcircuits.

The release of relay S2, the gain-maintaining relay, connects groundthrough the left-hand armature to a resistance R6 associated with thecondenser C1 of the gain-control circuit. This connection permits thenormal action of the gaincontrol circuit while the carrier is beingreceived; also the position of the left-hand armature of relay S2 causesrelay S3, the quick gain control relay, to be released.

As indicated above, the voltage set up in resistance R1, when thecarrier is received, acts on the automatic gain control circuit throughtube T1. The negative voltage in the resistance tends to lower thecurrent in tube T1 and thereby results in the lowering of the current inresistance R2 and the reduction of the negative voltage applied to` thegrid of the tube T2. Thus, the 5 plate current of tube T2 tends toincrease, with the resultant tendency to charge the condenser C1 throughresistance R3, the upper side of the condenser being charged to anegative value with respect to ground. It will be understood that tubesT1 and T2 form a second stage of the gain control circuit, through whichstage there is directly exercised an appropriate control of the gridvoltages of the vacuum tubes constituting the high frequency amplier,the iirst detector and the intermediate frequency amplifier of thereceiver proper. It will be understood further from the discussionalready had and from an examination of the batteries included in thecircuit that the arrangement disclosed tends to maintain a constantoutput of carrier from the second detector; if this output becomes toohigh, the increased negative voltage in resistance R1 results in thecharging of condenser C1 and the increase of the negative voltage on thegrids of the receiver tubes. If, on the other hand, the carrier outputbecomes too low, condenser C1 discharges through resistances R4 and Reand the left-hand armature of relay S2, and the negative bias on thereceiver tube grids is reduced, with the result of an increased gain.Resistance R3 tends to slow down the charging of condenser C1 whileresistances R4 and Re tend to delay the discharge of that condenser. Thenet result of the operation of this gain control circuit is that thecarrier output of the second detector tends to remain constant.

If, now, the reception of carrier energy ceases, the current inresistance R1 drops to Zero, the negative bias on the grid of tube T isremoved o and plate current flows in this tube and through the windingsof' relays S1 and S2. The operation of relay S1 places a short circuiton the audiofrequency amplier output or path L and thus, in the absenceof carrier and signal transmis- 5 sion, interfering energy cannot passon over the receiving circuit.

When relay S2 operates its left-hand armature, ground is removed fromresistance Rs and the I further discharge of condenser C1 isprevented.`50 This relay operation also connects ground to resistance R1and a second condenser C2 starts to discharge through that resistance.This discharge, if continued, will cause the operation of the quick gaincontrol relay S3. It will be noted 65 that the current through thewinding of this relay is that produced by the difference between thevoltage from the battery B1 associated with resistance R5 and thevoltage of condenser C2. It A should be noted at this point that since,with the removal of the carrier and the operation of relay S2, thecondenser C1 can no longer discharge, the gain of the receiver will bemaintained at a substantially constant value, some slight allowancebeing made for the gradual leakage of the charge on condenser C1; inother words, the receiver gain is maintained at a predetermined value,that is at the setting last established by the operation resulting fromthe reception of the carrier energy.

As has been indicated hereinabove, it is desirable that the gainadjusting action be relatively slow in order to prevent excessivehunting of the gain control devices and the resultant distortion.Accordingly, when the carrier comes on again, it may be an appreciable,time before the receiverfgainwill be adjusted to prevent distortion,since the value 4,of there-applied carrierv may be widely dierentfromthat obtaining before the cessation of carrier reception. To avoid .thisdifficulty, the applicant provides for the abnormal, quick adjustment ofthe receiver gain when the carrier is again received. To accomplish thisquick adjustment isthe function of the` relay S3. After the removalofthe carrier and the effective discharge of condenser C2, relay S3operates and placesa short circuit around resistances R3 Vand R4.Accordingly, when the carl rier again cornes on, the gain controlcircuit will quickly adjust the receiver .gain V to meet anyA changebetween the new carrier valueV and the old. As has been indicated above,relay Ss is made slow operating and slow releasing. The relay shouldoperate slowly so that when the carrier is merely interrupted for a veryshort period instead of actuallybeing removed fora consid-.q

erable period, the gain control apparatus will function in the normalmanner; the relay should release slowly so that when the carrierreappears after a substantial interval, the quick adjusting feature willbe maintained long enough to permit` the receiver to become adjusted tothe new carrier value. `After that Yfunction `has been performed, ofcourse, relay S3 releases and the gain control circuit functionsnormally until after the carrier is again removed.

The action of the quick Vgain control relay S3 will now be consideredin, further detail. The

" time actions o-f this relay .are affected by resistances R5 and R1 andthe` condenser C2; When relay Sz first operates after an extended periodof release, condenser l `Cz startsA 4to discharge through resistance`Rr. Previously, this condenser has been charged to thevalue of batteryB1 associated with resistance R5. `If relay S2 is` operated only for ashort period, the discharge of condenser C2 will be slight and thecurrent flowing through resistance R5 andthe winding of relay S3 will besmall, since, as stated above, this current depends on the differencebetween the voltage of battery B1 andthe charge on condenser Cz andrelay S3 will not o-perate.V If relay Sz operates for a suicient time todischarge C2 as far as possible, however, the current in relay -Ss willbe more than suicient to operate it.. Y The joint action of resistanceR5 andV condenser C2 then serves to delay therelease Vof relay S3 for asho-rt period after relay Sz releases.

It may be desirable in certain cases to have the receiver gain `set atsome predetermined value other than the last value produced by the gaincontrol circuit when the carrier is` removed for more than apredetermined time. It would probably not be desirable to set thereceiver at its 'fixed gain when the carrier dropped out for only ashort interval.V For such modified operation, there is added to therelay S2 a right-hand armature and, furthermore, a relay S4 andanadjustable battery B2 are added, along with resistances Re and R9 andcondenser C3. .Relay S4 controls the connection of a battery Bz toresistance R6.` While carrier `is being received, the right-handarmature of relay S2 is against its contact and a circuit is completedthrough the winding of relay S4. As long as this condition obtains,thecircuit between battery B2 and resistance Re is broken..A If,however, the carrier is removed and the. armatures of relay S2 are,separated from'. their back` contacts, relay S4. eventually releases andbattery B2 is connected through resistance Re to thecondenser C1 of thegain control circuit. The time required for relay S4 to release iscontrolled bythe time required forcondenser VC3 to be charged up throughRs and the winding of S4. Resistance R9 is corn- 5^ paratively small and.is used toprevent burning of the contacts oflvrelay S4. YWith theadjustment of battery B2, the receiver gain setting can thus be broughtback to any suitable predeteri, mined value. The product RsXCs should be1d greater thanRsXCz or R7 C2.

As has been stated hereinbefore, the applicants invention is Vapplicablenot only to the case of vcontrol of thereceiving circuitsby the carrierbut also to the case of such control by any other control energy ofspecial frequency. In the later case, the receiverarrangement forcontrolling the voltage in resistance R1" may be modified to take theform indicated inlFig. 3, `in which the n, control energy taken from theoutput of the sec- 20 ond detector mustpass through a band-pass filter Fand operate a rectifier tube RTbefore there is any effect on resistanceR1. l It will be understood thatf once the effect is produced inresistance R1, the operation of thezcircuit as modified in ac- 25'Vcordance with Fig. 3 follows that of the circuit of Fig. 2.

While the invention has been disclosed specifically for the purpose ofillustration, it is to be Vunderstood that it may take many ,other and30 widely diiferent forms within the spirit of the invention as definedby the appended claims.

What is claimed is:

1. In a system ,for the reception of signals, including a receiver'` andmeans responsiveto the 35 reception and non-'reception of distinctiveenergy for governing the receiver, the method of transmission controlwhichconsists in adjusting the gain of the receiver while the. governing,energy is being received in accordance with the intensity 40 ofsaidenergy, and in theabsence of said energy maintaining said gain at thevalue last established for a time not in excess of a predeterminedperiod.

2. In a system for the reception. of signals, including a receiver andmeans responsive to the reception and non-reception of distinctiveenergy for governing the receiver, the method of transmission controlwhich consists in adjusting the gain of the receiver while the governingenergy is being received in accordance with the intensity of saidenergy, maintaining said gain at the value last established while thereception of said energy is absent for a predetermined or shorter time,and setting said gain at a predetermined value at the expiration of saidpredetermined time if `the absence of the governing energy continues.

3. In a system for the reception of signals, including a receiver andmeans responsive to the reception and non-reception of` distinctiveenergy 60' for governing the receiver, the method of transmissioncontrol which consists in adjusting the gain of the receiver while thegoverning energy is being received in accordance with the intensity ofsaid energy, normally retarding the gain ad- 55 justing action, settingsaid gain at a suitable value in the absence of said energygandtemporarily speeding up the gain adjusting action .after the absence ofsaid energy has continued for a predetermined time.

4. In a system for the transmission of signals, including a transmittingstation and a receiving station, the method of transmission controlwhich consists in sending from the transmitting station during theperiods of signal transmission control 15 20,., ergy is removedfor.a'considerabletime, and after i only during the periods of signaltransmission,

energy of a, distinctive frequency, adiustingthe gain 'atA thefreivrig.V station lwhilefsai'd; control energy is being vreceived inilaccordance"y with the intensity of said energyl, lormallyretarding the,Y gain adjusting action,"'maintainingv 'said' gain, during the periods`when, no' control 'energy isA being received, at the value 'last`-established, and temporarily speeding up. the gain adjusting actionafterthre absenceoffthe contrl'energyhas continued for a predeterminedtime.

5. In a system Afor the transmission of signals, including atransmittingl station and a'receiving station, the method oftransmission control which consists in sendingv from the transmittingvstation during the periodsv of signal transmission control energy of adistinctive `Afrequency, adjusting the gain at the receivingstationWhile said control energy is being received in accordance with theintensity of said energy, maintaining said gain at the value lastestablishedif. the control enthe absence of the control energy hascontinued for a predetermined timejsetting' said gain at a predeterminedvalue'.

6. In a system for the transmission of signals,

" including a transmitting station and a receiving station, the methodof transmission control 4which consists in sending from the transmittingstation control energy' of a distinctive frequency, ad-

justing the gain at the receiving vstation while said control lenergy isbeing received in accordance with the intensityfof said energy,maintaining said gain at the value lastestablishedfif the control energyceases, for a considerable time, setting said r gain at a predetermined'value after the control energy hsbeeh absent. fQl 1 redetemineid time,and quickly readjiistingsjaid gain when 'the control energyl isren-applied tothe system..

7. In a 'system for" the' reception of signals, including a receiver anddemodulated signal path associatedY therewith, the' methndoftransmission control which consists in applying control energy of adistinctive frequency to the "system only during the periods of signal'transmission, providing for the adjustmentof the receiver ain while thecontrol energy'is beingv received' in accordance maintaining saiddemodulated signal path in a condition of disability when said'controlenergy is not being received, causing the reception of said controlenergy to rendersaid path operative,

providing for the adjustment o f the receiver gain while the controlenergyis being received inv accordance with the intensity of saidenergy, setting said gain at a suitable value when the control energy isremoved from the system for a considerable time, and quickly renderingsaid adjustment eilective when the control energy is reapplied to thesystem after a substantial interruption, even though the value of saidenergy has changed to a considerable degree.

were@ 9- In.A @Signaling syslemneludns a transmitting ,stationanda'receiving station, means at'the transmitting stationunderthecontrol of the signal energy forapplying to the system controlenergyof a distinctive frequency, means at the receiving stationcontrolled by the received controlenergy for regulating the gain of thereceiver, means for normally retarding the action of the gain regulatingmeans, means responsive to the cessation of the reception of saidcontrol energy for maintaining said gain attthe value lastestablishedyand means responsive to the absence of saidcontrol energybeyond a predetermined time for temporarily disabling the retardingmeans.

10. Inr a signaling system including a transmitting station and areceiving station, means at the transmittingstation under the control ofthev signal energy for applying tothe system control energy of adistinctive frequency, means at the' receiving station controlled by thereceived control energy for regulating the gain of the receiver, meansresponsive to a cessation of the` reception of the control energy formaintaining said gainat the value last established, and means responsiveto the absence of the control energy beyond a predetermined time forsetting the receiver gain at a predetermined value.

11. In a signaling system including a transmitting station and areceiving station, means at the 'transmitting station under the controlof the signal energy for applying to the system control energy of adistinctive frequency, means at the receiving station controlled by thereceived control energy for regulating the gain of the receiver, meansresponsive to the cessation of the reception of control energy formaintaining said gain at the value last established, means responsive tothe absence of the control energy for longer than a predetermined timefor setting said a demodulated signal path, said path being normallymaintained in a condition of disability,

40k gainv at a predetermined value, and means for i" means at thetransmitting station under the control of the signal energy for applyingto the system control energy of a distinctive frequency,

means at the receiving station responsive to the reception of saidcontrol energy for removing the disability from said demodulated signalpath, means at the receiving station controlled by said control energyfor regulating the gain of the receiverv in accordance with theintensity of said energy, means for normally retarding the action of thegain regulating means, means for setting the receiver gain at a suitablevalue during the absence of thecontrol energy,'and means responsive tothe absence of the control energy beyond a predetermined time fortemporarily disabling the retarding means.

13. In a system for the reception of signals, including a receiver and ademodulated signal path associated therewith, the method of transmissioncontrol which consists in maintaining the demodulated signal path in acondition of disability when no carrier energy is being received,causing the reception of carrier energy to render said path operative,adjusting the gain of the receiver whilethe carrier energy is beingreceived in accordance With the intensity of said energy, normallyretarding the gain adjusting action, maintaining said vgain atthe valuelast established 'which' consists in maintaining the demodulatedVwhenthe reception of carrier energy ceases, and

temporarily speeding up the gain adjusting ac- K tion after the absenceof carrier energy has continued for a predetermined time. p

. 14. In a system for the receptionl of signals, including a receiverand a demodulatedsignal path associated therewith, the method oftransmission control which consists in` adjusting the gain of thereceiver whilecarrier energy is being received in accordance with theintensity of said energy, maintaining said gain at the value lastestablished while the carrier energy is absent for a predetermined orshorter time, setting said gain ata predetermined value if the absenceoi carrier energy continues beyondsaid predetermined time and quicklyreadjusting said .gain when said reception issrenewed. l,

' 15. In a system for the reception of carrier Venenergy to be modulatedbysignals, including a receiver and ademodulated signal path associatedtherewith, the method of transmission control which consists inadjusting the gain of the receiver while carrier energy is beingreceived in accordance with the intensity of said energy, and in theabsence of said energy maintaining said gain at the value lastestablishedfor a time not in excess of a predetermined period.:

16. In a system for Athe reception of carrier energy to be modulated bysignals, including a receiver and a demodulated signal path associatedtherewith, the method of transmission control which consists inadjusting the gain of ,thereceiver while carrier energy is beingreceived in accordance with the intensity of said energynormallyretarding the gain adjusting action, maintaining said gain at the valuelast established if the reception of the carrier energy is ,absentfor atime not in excess of `a predetermined period, and temporarily speedingup thegain adjusting action after the absence of` carrier energy hascontinued fora predetermined time. Y

' 17. In a system for the reception of carrier energy to be modulated bysignals, including a receiver and a demodulated signal path associatedtherewith, the method `of transmission control which consists inmaintaining the demodulated signal path in a condition of disabilitywhen no Y carrier energy is being received, causing the reception ofcarrier energy to render said path operative, .adjusting the 'gain ofthe receiver while thecarrier energy is being received in accordancewith the intensity of said energy, and in the absence of said energymaintaining said gain at the value last established `for a time not inexcess of a predetermined period.

18.In a system for the reception of signals, including a receiver and ademodulated signal path associated therewith, the method` oftransmission `control which consists in maintaining the demodulatedVsignalpath in a `condition of d isabilitywhen no carrier energy isbeing received, causing the reception of carrier energy to render saidpath operative,. adjusting the gain of the receiver while the carrierenergy is being received in accordance with the intensity of saidenergy, maintaining saidgain at the value last established while thecarrier energy is absent for a predetermined or shorter time, Vandsettingsaid gain at a predetermined value if the absence of carrierenergy continues beyond said predetermined time. l. l

19. In a system for the` reception of carrier energy to be modulated bysignals, including a receiver and a demodulated signal path associated 5therewith, the method of transmission control signal path in a conditionof `disability when no carrier energy is being received,.causingthereception of carrier energy to render said path operative, adjustingthe'gain-of the receiver while the carrier energy is being received inaccordance withtheintensityof said energy; normally retarding the gainadjusting action, in the absence of the carrier energy maintaining saidgain at the value last established ior a time` not in excess of apredetermined period, setting said gain at a predetermined value if; theabsence'o carrier energy continues beyond' said predetermined period,and temporarily speeding up the gain adjusting action after the absence4of the carrier energy has continued for a predetermined time.

20; In a system for the reception of carrier energy to be modulated bysignals, including a receiver and a demodulated signal path associated vhas greatly changed.

21.In a system forthe reception of carrier D energy to be modulatedbysignals, including a receiver and a demodulated signalpath associatedtherewithythe method of-transmission control which consists in providingfor the adjustment of the receiver gain 4while carrier` energy is beingreceived in accordance with the intensity of said energy, normallyretarding the gain adjusting action, setting said gain at a suitablevalue in the absence of carrier energy, and itemporarily speeding up thegain adjusting action after the absence of carrier energy has continuedfor `a predetermined time.

22. Inasystem for thereception of acarrier wave to be modulated bysignal energy, a receiver having a demodulated signal path associatedtherewith, means controlled by carrier energy transmitted to thereceiver for regulating the gain of the receiver, and means responsiveto the cessation of the reception ofcarrier energy for maintaining saidgain atthe value last established for a time not in excess of apredetermined period.

23. In a system for the receptionl of a carrier wave to be modulated bysignal energy, a receiver having a, demodulated signal path associatedtherewith, means controlled by carrier energy transmitted to thereceiver for regulatingthe gain of the receiver, means for normallyretarding the action of the gain regulating means, means responsive tothe cessation of the reception of carrier energy for maintaining saidgain at the value last established, and means responsive to the absenceof carrier, energy beyond a predetermined time for temporarily disablingthe l retarding means.

the absence of carrier energy continued beyond said predetermined timefor setting said gain at a predetermined value.

25. In a system for the reception of a carrier Wave to be modulated bysignal energy, a receiver having a demodulated signal path normallymaintained in a condition of disability, means responsive to carrierenergy transmitted to the receiver for removing the disability from saidpath, means controlled by said carrier energy for regulating the gain ofthe receiver in accordance with the intensity of said energy, means fornormally retarding the action of the gain regulating means, meansresponsive to the cessation of the reception of carrier energy formaintaining said gain at the value last established, and meansresponsive to the` absence of carrier energy beyond a predetermined timefor temporarily disabling the retarding means.

26. In a system for the reception of signal energy, a receiver having ademodulated signal path normally maintained in a condition ofdisability, means responsive tocarrier energy transmitted to thereceiverfor removing the disability from said path, means controlled by saidcarrier energy for regulating the gain of the receiver in accordancewith the intensity of said energy, means responsive to the cessation ofthe reception of carrier energy for maintaining saidgain at the valuelast established, means responsive to the continuation ofthe absence ofthe carrier energy beyond a predetermined time for setting said gain ata predetermined value, and means for quickly readjusting said. gain whenthe reception of carrier energy is renewed. Y

27. In a system for the 'reception of a carrier wave to be modulated bysignal energy, a receiver having a demodulated signal path associatedtherewith, means controlled by carrier energy transmitted to thereceiver for regulating the gain of the receiver in accordance with theintensity of said energy, means'for normally retarding the actionof thegain-regulating means, and means responsive to the absence of carrierenergy beyond a predetermined 'time for temporarily disabling theretarding means.

28. In a system for the reception of a carrier wave to be modulated bysignal energy, a receiver having a demodulated signal path associatedtherewith, means controlled'byl carrier energy transmitted to thereceiver for regulating the gain of the receiver in accordance with theintensity of saidk energy, and means responsive to the cessation of thereception of carrier energy for maintaining said gain at the value lastestablished for a time notin excess of a predetermined period.

29. In a system for the reception of a carrier wave to be modulated bysignal energy, a receiver having a demodulated signal path normallymaintained in a condition of disability, means responsive to carrierenergy transmitted to the receiver for removing the disability from saidpath, means controlled by said carrier energy for regulating the gain ofthe receiver in accordance with the intensity of said energy, and meansresponsive to the cessation of the reception of carrier energy formaintaining said gain at the value last established for a time not inexcess of a predetermined period.

30. In a signaling system, a transmitting station, a receiving stationincluding a receiver and a demodulated signal path, means at thetransmitting station under the control of the signal energyforapplyingcarrier energy tothe system,

means at the receiving station controlled by the received carrierenergy' for regulating the gain `of the receiver, and means responsiveto the cessation of the reception of carrier energy for maintaining saidgain at the value last established for a time not in excess of apredetermined period.

31. In 'a signaling system, a transmitting station, a receiving stationincluding a receiver and a demodulated signal path, said path being nor-10 mally maintained in a condition of disability. means at thetransmitting station under the control of the signal energy for applyingcarrier energy to the system, means at the receiving station responsiveto received carrier energy for removing the disability from saiddemodulated signal path, means at the receiving station controlled bysaid carrier energy for regulating the gain of the receiver inaccordance with the intensity of said energy, means for maintaining thereceiver gain at the last established value when the reception of thecarrier energy ceases, means responsive to the absence of thecarrierenergy continued beyond a predetermined time for setting said gain at apredetermined value, and means for quickly readjusting said gain whenthe reception of the carrier energy is renewed.

32. In a receiver of signal energy, means responsive to incoming energyfor regulating the gain of the receiver, means for normally retardingthe action of the gain regulating means, and means responsive to theabsence or incoming energy beyond a predetermined time for temporarilydisabling the retarding means, whereby the subsequent renewal of theincoming energy will produce immediate readjustment of the gain of thereceiver.

33. In a receiver of signal energy, means responsive to incoming energyfor regulating the gain of the receiver, means for normally retardingthe action of the gain regulating means, means responsive to thecessation of incoming energy for setting the gain of the receiver at asuitable value, and means responsive to the absence of incoming energybeyond a predetermined 45 time for temporarily disabling the retardingmeans, whereby the subsequent renewal of the incoming energy willproduce immediatevreadjustment of the gain of V.the receiver.

34. In a receiver of signal energy, the method of transmission controlwhich consists in adjusting the gain of the receiver in accordance withthe intensity of incoming energy, normally retarding the gain adjustingaction,and providing for the temporary withdrawal of the retardation ofthe gain adjusting actionv after the absence of incoming energy hascontinued for a predetermined time, whereby the subsequent renewal ofthe incoming energy will produce immediate readjustment of the gain of-thereceiven 35. In a receiver of signalenergythe method of transmissioncontrol which consistsin adjusting the gain of the receiver inaccordance-with'the intensity of incoming energy, normally retarding thegain adjusting action, setting the gain of thereceiver ata suitablevalue in the absence' of incoming energy, and providing for thetemporary withdrawal'of the retardation of the gain adjusting actionafter the'absence of incoming energy has continuedfor a predeterminedtime, whereby the subsequent renewal of the incoming energy will produceimmediate` readjustment of the gain of the receiver,

DOREN MITCHELL.

